Complex disaster has disabled the ordinary communication system. For example, fire on LTE routers and their power supply interrupted communication. In our disaster react robot system, we suggested a portable and battery-powered Wi-Fi module dropped by reconnaissance robots. As a result, the communication speed was extremely limited. In this paper, we proposed a global map generation strategy to overcome this communication limit. Our key approach involved the conversion of heterogeneous local maps to 2D occupancy grid maps. The 2D map was treated as an image and image stitching algorithm was applied to build the global map. We made various local map scenarios and applied our global map building algorithms. In conclusion, our proposed strategy was verified with the real robot test.